trying to understand m4 feed ramp cut vrs extension

rookie5.56 · October 5, 2011, 04:02 PM

which is better having a barrel cut to have m4 feed ramps or putting an extension on with the m4 feed ramps? wanting to run a dpms fluted bull but the receiver I bought has m4 feed ramps the barrel does not. Has anyone done this yet and what is the cost factor?

tobnpr · October 9, 2011, 09:12 AM

This should help explain, and answer your question:
http://www.m4carbine.net/showthread.php?t=193

Not sure what you mean about having the "barrel" cut for feed ramps-they're always a part of the extension, not the barrel itself (?)

rookie5.56 · October 9, 2011, 01:54 PM

some barrels i have seen mention there allready cut with m4 feed ramps the extension. I'm looking for a fluted bull barrel. trying to see whats better the ramps being cut in or the extension being replaced.

DnPRK · October 9, 2011, 02:14 PM

Once the gas port has been drilled, it is extremely difficult to replace an extension (and expensive if you can find someone willing to do it).

Your best bet is to enlarge the feed ramps on your existing extension to match the receiver's M4 cuts.

NWPilgrim · October 9, 2011, 03:21 PM

If only one is cut for M4 feed ramp, the barrel extension or the receiver, it is better for it to be the barrel. If you have the receiver cut and NOT the barrel extension then there is a sharp ledge the bullet encounters at the end of the receiver cut.

If it is the other way around then the receiver has no cut and the bullet encounters a drop off at the joint between receiver and barrel extension (where the barrel extension cuts begin). A drop off will not affect feeding because the bullet has already been raised up enough to clear the initial receiver edge.

I would see if you can exchange the upper receiver for one without the M4 ramp cuts. Those are only needed really for the shorter carbine gas system and mostly for full auto reliability. Most barrels 16" or less will have the barrel extension cuts. Fewer barrels over 16" will have the cuts. I just bought a Palmetto State complete FN upper that has the M4 cuts in both, and BCM offers a 20" with M4 cuts in both, but that is unusual.

rookie5.56 · October 11, 2011, 12:52 PM

yeah exchange isnt a option , looks like I'll have to find a 16 inch bull barrel with the m4 cuts or have someone cut it. picked up the reciever at a show spikes tact. with dust cover and forward assist installed for 90

DnPRK · October 11, 2011, 10:04 PM

The link is to a stripped receiver without the M4 cuts. The last several I bought were made by Cerro Forge and fit perfectly.
http://www.jsesurplus.com/flattopupp...rstripped.aspx

October 5, 2011, 04:02 PM	#1
rookie5.56 Member Join Date: October 1, 2011 Posts: 21	trying to understand m4 feed ramp cut vrs extension which is better having a barrel cut to have m4 feed ramps or putting an extension on with the m4 feed ramps? wanting to run a dpms fluted bull but the receiver I bought has m4 feed ramps the barrel does not. Has anyone done this yet and what is the cost factor?

October 9, 2011, 03:21 PM	#5
NWPilgrim Senior Member Join Date: September 29, 2008 Location: Oregon Posts: 2,346	If only one is cut for M4 feed ramp, the barrel extension or the receiver, it is better for it to be the barrel. If you have the receiver cut and NOT the barrel extension then there is a sharp ledge the bullet encounters at the end of the receiver cut. If it is the other way around then the receiver has no cut and the bullet encounters a drop off at the joint between receiver and barrel extension (where the barrel extension cuts begin). A drop off will not affect feeding because the bullet has already been raised up enough to clear the initial receiver edge. I would see if you can exchange the upper receiver for one without the M4 ramp cuts. Those are only needed really for the shorter carbine gas system and mostly for full auto reliability. Most barrels 16" or less will have the barrel extension cuts. Fewer barrels over 16" will have the cuts. I just bought a Palmetto State complete FN upper that has the M4 cuts in both, and BCM offers a 20" with M4 cuts in both, but that is unusual. __________________ "The ultimate authority ... resides in the people alone. ... The advantage of being armed, which the Americans possess over the people of almost every other nation ... forms a barrier against the enterprises of ambition." - James Madison

October 9, 2011, 09:12 AM	#2
tobnpr Senior Member Join Date: August 1, 2010 Location: Tampa Bay Posts: 4,556	This should help explain, and answer your question: http://www.m4carbine.net/showthread.php?t=193 Not sure what you mean about having the "barrel" cut for feed ramps-they're always a part of the extension, not the barrel itself (?)

October 9, 2011, 01:54 PM	#3
rookie5.56 Member Join Date: October 1, 2011 Posts: 21	some barrels i have seen mention there allready cut with m4 feed ramps the extension. I'm looking for a fluted bull barrel. trying to see whats better the ramps being cut in or the extension being replaced.

October 9, 2011, 02:14 PM	#4
DnPRK Senior Member Join Date: August 24, 2001 Location: LC, Ca Posts: 1,917	Once the gas port has been drilled, it is extremely difficult to replace an extension (and expensive if you can find someone willing to do it). Your best bet is to enlarge the feed ramps on your existing extension to match the receiver's M4 cuts.

October 11, 2011, 12:52 PM	#6
rookie5.56 Member Join Date: October 1, 2011 Posts: 21	yeah exchange isnt a option , looks like I'll have to find a 16 inch bull barrel with the m4 cuts or have someone cut it. picked up the reciever at a show spikes tact. with dust cover and forward assist installed for 90

October 11, 2011, 10:04 PM	#7
DnPRK Senior Member Join Date: August 24, 2001 Location: LC, Ca Posts: 1,917	The link is to a stripped receiver without the M4 cuts. The last several I bought were made by Cerro Forge and fit perfectly. http://www.jsesurplus.com/flattopupp...rstripped.aspx